Extraclassical inhibition (ECI) in the retina and lateral geniculate nucleus (LGN) acts to suppress responses to stimuli presented in the classical receptive field (CRF). Here we asked 1) do koniocellular (blue-on and blue-off) cells exhibit ECI? 2) does the ECI show chromatic selectivity? 3) what is the relative strength of short-wavelength sensitive (S, “blue”) and medium/long wavelength sensitive (ML) cone inputs to CRF and ECI? We recorded extracellular action potentials from the LGN of sufentanil-anesthetized marmosets. Weights of S and ML cone inputs were measured using 1) cone-selective and achromatic stimuli presented in variable apertures and annuli, 2) modulation in an ML/S color plane [1], and 3) modulation of chromaticity and luminance through the D65 white point [2]. We found ECI in all cell classes is dominated by ML cone inputs. Average response attenuation (S-cone selective annuli vs. achromatic annuli) was 6% vs. 52% for PC cells (n=50), 20% vs. 63% for MC cells (n=10), 20% vs 45% for blue-on cells (n=21), and 19% vs. 43% for blue-off cells (n=3). The MC and PC cells we recorded only rarely received detectible input from S cones. Where detectible, S cone inputs mostly influenced PC cells, and were weak and inhibitory. We conclude that S cone signals are functionally isolated to the classical receptive field of blue-on and blue-off cells in the LGN.